Aviadenoviruses can be subdivided into three groups:
Group I adenoviruses, a subclass of which comprises the fowl adenoviruses (FAV) having a genomic DNA length of .+-.43.8 kb and two fibres protruding from one pentonbase. The Group I viruses share a common antigen (`group antigen`) which distinguishes them from Group II and Group III viruses (ref. 1,9). PA1 Group II adenoviruses, having Group II specific antigen, comprise a small number of viruses, such as the turkey Haemorrhagic Enteritis virus. These viruses have a genomic DNA length of .+-.25.5 kb and sport one fibre per penton base. PA1 Group III adenoviruses, of which the Egg Dropping Syndrome causing virus (EDS) is the only serotype, have a genomic DNA length of 33.2 kb and a single fibre per penton base. EDS is serologically not directly related to Group I viruses (ref. 11).
Group I adenoviruses can be isolated from different avian species and have been classified as Fowl adenoviruses (FAV), Goose adenoviruses (GAV), Duck adenoviruses (DAV) and Turkey adenoviruses (TAV). The length of the two fibres of FAVs is different for each of the 12 serotypes. In addition to serological typic, the viruses can be characterized by analysis of their DNA. Based on BamHI and HindIII cleavage of the DNA of FAV serotypes 1-11, five subgroups are recognized (ref. 1,4,6,9).